A semiconductor-element mounting member (e.g., a submount, a heat spreader, a heat sink, or a housing) which has an element mounting surface on which a semiconductor element, such as a light emitting diode or a semiconductor laser, is mounted and used is required to have a high thermal conductivity.
Heat generated during the operation of the semiconductor element can be promptly removed through the semiconductor element mounting member by giving such a high thermal conductivity to the semiconductor element mounting member. Therefore, the semiconductor element can be prevented from making a malfunction caused by heat, or from lowering its operation efficiency and its lifetime, or from being damaged.
Conventionally, the semiconductor element mounting member has been generally made of ceramic such as AlN or SiC. However, in recent years, with the heightening of the output capability of the semiconductor element, the semiconductor element mounting member has been required to have an even higher thermal conductivity.
In order to fulfill this requirement, in recent years, a semiconductor element mounting member that consists of a diamond-metal complex including many fine diamond particles and a matrix metal has been developed. Diamond has the highest thermal conductivity of all substances, and therefore the thermal conductivity of the semiconductor element mounting member is expected to be made enormously higher than conventional ones made of ceramic or the like by forming the semiconductor element mounting member by use of the diamond-metal complex.
For example, Published PCT International Application No. WO03/040420 (“Patent Document 1”) discloses a production method mentioned below according to which a semiconductor element mounting member that consists of a diamond-metal complex is produced.
A mixture of diamond particles each of which has a particle diameter of from 5 μm to 100 μm, a Cu powder, and a Group IVa (Ti, Zr, Hf) or Group Va (V, Nb, Ta) metal powder is enclosed in a metallic capsule in a vacuum or in an inert atmosphere.
Thereafter, the metallic capsule is subjected to heat treatment and pressure treatment under a high-temperature/extra-high-pressure condition under which the pressure ranges from 1 GPa to 6 GPa, and the temperature ranges from 1100° C. to 1500° C.
As a result of the heat treatment and the pressure treatment, the many diamond particles are connected together by means of Cu that has been forcibly infiltrated between the diamond particles. In this case, the mixture mixing ratio and the high-temperature/extra-high-pressure condition are set so that at least several diamond particles are kept in direct contact with each other.
Thereafter, the metallic capsule is removed by, for example, grinding, and then a precursor of a semiconductor element mounting member that consists of the diamond-metal complex is obtained, and the resulting precursor is subjected to electric discharge machining if necessary, thus producing a semiconductor element mounting member that has a predetermined three-dimensional shape.
However, in this production method, special manufacturing facilities that can create the high-temperature/extra-high-pressure condition are needed, and therefore the restriction of the manufacturing facilities imposes inevitable limitations on the size of a producible semiconductor-element mounting member. In a state of the precursor that has not yet been subjected to, for example, electric discharge machining, the limit of its size is about diameter 70φ×thickness 5 mm.
Additionally, the heat treatment and the pressure treatment are performed according to so-called batch processing, and require much time for one-time processing, and consume enormous energy, and therefore the productivity of the semiconductor element mounting member is remarkably low.
Additionally, large-scale manufacturing facilities are needed in comparison with the size of a precursor that can be formed, and, as a result, disadvantageously, production costs of the semiconductor element mounting member become high.
Japanese Published Unexamined Patent Application No. H10-223812 (“Patent Document 2”) discloses a production method mentioned below according to which a diamond-metal complex is produced.
In a state in which a container is filled with many diamond particles each of which has a particle diameter of from 60 μm to 700 μm, Groups 4A to 7A metals, such as Ti, Zr, and Hf, are infiltrated, and a layer made of carbide of the metals is formed on the surface of the diamond particles.
Thereafter, Cu, Ag, Au, Al, etc., are further infiltrated into gaps between the many diamond particles so as to function as a joining material, thereby joining the many diamond particles together.
Japanese Published Unexamined Patent Application No. H11-80858 (“Patent Document 3”) discloses a production method mentioned below according to which a carbon-metal complex is produced.
The surface of a dispersing agent made of carbon and/or graphite is coated with a covering layer made of one or more elements, such as Cr, Fe, or Mo, by means of, for example, PVD, CVD, or plating.
Thereafter, the dispersing agent and a matrix metal (joining material) that is made of Cu or a Cu alloy are combined together.
In this production method, a diamond-metal complex can be formed by using diamond particles serving as a dispersing agent.
Both the carbide layer of Patent Document 2 and the covering layer of Patent Document 3 serve to improve the wettability of a melt of a metal, such as Cu, that is used as a joining material with respect to diamond particles. In other words, each of these layers functions as an infiltration auxiliary layer that assists the infiltration of the metal and the combination with the diamond particles.
Therefore, the infiltration step can be performed in a vacuum or in an inert atmosphere under approximately normal pressure, and large-scale manufacturing facilities and the like are not required to be used for creating the high-temperature/extra-high-pressure condition of Patent Document 1.
Therefore, limitations imposed on the size of a producible composite material can be substantially eliminated.
Moreover, the covering-layer coating process, as well as the infiltrating process, can be performed in a shorter time and with enormously less consumption energy than the heat treatment and the pressure treatment under the high-temperature/extra-high-pressure condition.
Especially the infiltration step can be continuously performed by use of, for example, a belt furnace.
Therefore, according to the production methods of Patent Documents 2 and 3, advantageously, the semiconductor element mounting member can be produced with extremely excellent productivity and at extremely low cost.
However, a problem resides in the fact that, although the semiconductor element mounting member that is produced through the infiltration step of each of Patent Documents 2 and 3 is formed by use of diamond particles, the semiconductor element mounting member cannot obtain a high thermal conductivity resulting from the use of diamond particles.
The cause is that the infiltration auxiliary layer formed on substantially the whole of the surface of diamond particles hinders the diamond particles from coming into direct contact with each other, and hence brings about a decrease in thermal conductivity between the diamond particles.
Another problem resides in the fact that the number of process steps is increased, and the productivity of the semiconductor element mounting member is lowered in accordance with the necessity of the process of forming the infiltration auxiliary layer on the diamond-particle surface.